I have a 1989 Volvo 740. Several days ago its engine started acting weird. When on idle (either cold or warm) it runs at 1.2-1.4k rpm (used to run at 1k). When i turn throttle a bit it runs smoothly until it reaches like 1.4-1.5k rpm. Once rpm steps over that boundary, engine's rmp will start to cycle from 1.1-1.2k to 1.6-1.7k and back every 5-6 seconds (full cycle from 1.1 to 1.6 and back takes approximately that long and then it repeats).

Each time i clear error codes and run engine for a little while and then check codes again, i get 2-2-3 "Signal missing to/from IAC valve". Most of the times i get 2-3-2 "Fuel trim (lambda control) too lean or too rich at ide" as well.

I checked the valve. From the battery it opens once current is applied and "closes" when no current is applied. However once plugged to it's cable, it won't open when the key is on the 2nd (it's called "Ignition" i believe) position. Check with voltmeter. Current is present (probably due to partially discharged battery it gives me ~10V). Also if i understood correctly from the https://volvoforums.com/forum/volvo-...ymptoms-24535/ thread, when TPS clicks, voltage to IAC should drop significantly. It does not.

One more thing. IAC valve itself when in "closed" position overturns and opens up ~1 millimeter (~1/25") wide gap. Is that normal? Or should it close completely when no voltage is applied?

Thanks for any ideas, opinions, hints and advice in advance.

P.S. Hope i'm not duplicating topic. However my not too bad Google skills + terrible auto-mechanics knowledge + even worse auto-mechanics related English combination did not give any more ideas to try and check.

 

I'll just throw this one out there.

Have you checked the continuity of the IAC wires? They regularly don't fail, but There could be a bad connection. Do you have a wiring diagram for your fuel injection system? You need to see if you have Regina or Bosch fuel injection system. Look for your ignition coil under the hood. If it's a cylindrical one, it Bosch, if it's a funky square one, it's a Regina system.

 

Thanks Titan Joe. Any idea is better than none.... And it actually gave some results...

First of all, the ignition coil. I googled a bit for an image of it. Found this one: http://www.autopartswarehouse.com/im...d/siuf35_1.jpg (hope they won't mind me linking it here). Looks like the one i have in the passenger side back corner of engine compartment. Depending on your description it seems to be Bosh.

Now. The wiring. Found schematics on VOLVO 740 1989 - wiring diagrams and followed "LH-Jetronic 2.4, B230F" version. There seems to be a good connection all the way to ECU (especially since the cable actually gives current).
However, since i was at it, i checked TPS wiring as well, since it should switch on/off the current for IAC. Turns out, that "Throttle On" circuit within TPS itself is not working. Schematic shows pretty simple circuit inside. Is it possible to disassemble it and clean/fix it? or do i need another one?

One more thing. Amperage given to IAC is only 25mA... Is it just my imagination or is it way too low for the valve motor?